An Ancient Greek philosophical concept signifying a state of serene
calmness, unperturbedness, and complete freedom from distress or
worry.
It leads to calmness in difficult situations. It’s a bit like Stoicism or Buddhism. It’s
where worries and problems are just seen as totally natural and just
like breathing, where a lack of oxygen is dealt with by breathing,
problem-solving is just like that, no need to feel too much stress (it’s
just that problem-solving takes longer than breathing)